Helicopters are known comprising a fuselage; a main rotor mounted on top of a central portion of the fuselage; and an antitorque tail rotor for counteracting the torque transmitted from the main rotor to the fuselage.
Articulated main rotors and/or antitorque rotors are also known.
More specifically, articulated rotors comprise a drive shaft that rotates about a first axis; a hub that rotates integrally with the drive shaft about the first axis; and a number of blades projecting from the hub along respective second axes radial with respect to the first axis.
Each blade can rotate with respect to the hub about the respective second axis to vary its angle of attack with respect to the airstream, and can oscillate freely with respect to the hub about a respective third axis to perform a so-called flapping movement. Each third axis is crosswise to the first and second axis of the relative blade.
Each blade also oscillates freely with respect to the hub and the other blades about a respective fourth axis, parallel to the first axis, to perform a so-called lead-lag movement.
A need is felt within the industry to damp vibration induced by lead-lag movement of the blades over a wide range of drive shaft rotation speeds about the first axis, but without impairing aerodynamic performance of the rotor itself.